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Levelling @surveyingreport
- 1. JJOOMMOO KKEENNYYAATTTTAA UUNNIIVVEERRSSIITTYY OOFF AAGGRRIICCUULLTTUURREE AANNDD TTEECCHHNNOOLLOOGGYY Setting Trends in Higher Education, Research and Innovation School of Civil Engineering and Geospatial Engineering Bachelor of Geomatics Engineering and Geospatial Systems Bachelor of Geospatial Information Science INTERNAL ATTACHMENT Group 4 Fieldwork 2 Report LEVELLING Student Name Registration N尊 Gavin Kendo ENC221-0330/2016 Stildon Kimani ENC222-0337/2016 Tarri Halakhe ENC221-0159/2016 Calvin Kiplimo ENC222-0168/2016 Ivy Njeri ENC221-0157/2016 Raymond Rawlings ENC222-0362/2016 Sharon Mwanza ENC221-0098/2016 Barasa Samuel ENC222-0351/2016 Faith Mwende ENC221-0311/2016 Kosgei Antoney ENC222-0354/2016 Paul Akelo ENC222-0331/2016
- 2. Group 4 Fieldwork 2 Introduction Levelling is the determination of the relative heights (altitudes) of the different points in the area under survey, it is this information which, when coupled with that of the pan, enables a section through the land and/or artefacts to be drawn (Clancy, 1991). A horizontal line (or plane) of sight (line or plane of collimation) is established with a telescope (fitted with cross-hairs) which can be turned about a vertical axis. The difference in consecutive readings taken on a vertical staff gives the level difference between two points which can be seen in the figure below. Objectives: To determine the difference in level between points on the surface of the ground a 'series' of levels will need to be carried out; this is called a level traverse or level run. Able to adjust and check the levelling data.
- 3. Group 4 Fieldwork 3 Instruments to be used: 1. Level. 2. Staff. 3. Tripod. Figure 1 Procedure a) Set up the leveling instrument at Level position 1. b) Hold the staff on the Datum (RL+50 m) and take a reading. This will be a back sight, because it is the first staff reading after the leveling instrument has been set up. c) Move the staff to A and take a reading. This will be an intermediate sight. d) Move the staff to B and take a reading. This also will be an intermediate sight. e) Move the staff to C and take a reading. This will be another intermediate sight. f) Move the staff to D and take a reading. This will be a foresight; because after this reading the level will be moved. (A change plate should be placed on the ground to maintain the same level.)
- 4. Group 4 Fieldwork 4 g) The distance between the stations should be measured and recorded in the field book. h) Set up the level at Level position 2 and leave the staff at D on the change plate. Turn the staff so that it faces the level and take a reading. This will be a back sight. i) Move the staff to E and take a reading. This will be an intermediate sight. j) Move the staff to F and take a reading. This will be a foresight; because after taking this reading the level will be moved. k) Now move the level to Leveling position 3 and leave the staff at F on the change plate. l) Now repeat the steps describe 8 to 10 until you finished at point J. Sources of Error A problem we encountered during the practical was reading and booking errors. Many mistakes can be made during the booking of staff readings taken with a tilting level, and the general rule is that staff readings must be carefully entered into the levelling table or field book immediately after reading. We have done this practical twice, which is our first practical result was rejected. This is because the actual value is greater than allowable value. The next problem we faced was balancing the staff. When the reading is being taken, the staff is unbalanced due to the uneven ground surface and hot weather disrupted the holders concentration. Alas, we gave timed signals so that the staff holder can concentrate for a few seconds while the reading is being taken. The next problem is weather conditions. In strong winds, a level can become unstable because the line of sight is always moving and it is also difficult to hold the staff steadily. For these reasons, it is not possible to take reliable readings under these conditions which should be avoided when levelling. Therefore, we had to find the suitable time to carry out our fieldwork.
- 5. Group 4 Fieldwork 5 Conclusion In this fieldwork, the reduced level of Bench Mark (BM) 1 is given. The leveling process begins with obtaining the back sight (BS) of BM1 and the foresight (FS) of turning point (TP) A. Then the auto level is shifted to obtain the BS of TP A and the FS of TP B. This process is repeated by shifting the auto level to obtain the BS and FS of the following staff stations and lastly go back to BM1 to obtain its FS in order to calculate the error of misclosure. We used both the rise and fall method and the height of collimation method to calculate the reduced level of each staff station. The error of misclosure was -0.006mm and the acceptable range of error of misclosure was calculated using the 12+/- k formulae where k represents the number of set-ups, and the acceptable range of error of misclosure is +/-37.947mm. Thus, our leveling is acceptable. To distribute the error, the correction per set-up is calculated using the following formulae: Correction per set-up = Error of misclosure 歎 Number of set up